Applications of Remote Sensing Techniques in the Prediction of water gushing in the Dayaoshan Tunnel
Wang Yuming
Information Centre of Aerial Surveying and
Remote Sensing Techniques of Railway
23 Road Xijiaominxiang,
Beijing, China
Abstract
The Dayaoshan Tunnel, 14,295km in length, is the longest double-track railway tunnel in China. Located in northern Guangdong province, the tunnel passes through the Nanling Mountains. Dense jungles, thick overburdens and concealment of most geological features brought great difficulty in the engineering survey of the tunnel, but applications of multiple kinds of space and aerial remote sensing images in comparison, interpretation and analysis provided a scientific basis for the evaluation of the hydro geological conditions of the tunnel. During the survey of the Dayaoshan Tunnel, drilling did not reveal substantial groundwater, but the application of macroscopic features of remote sensing images in analyzing the geological structure in the central part of the tunnel indicated that the geological structure was complex and had adequate water-gushing conditions, thus furnishing information for the construction of the tunnel. There were six localities where there was significant water gushing, of which four were situated within the area extent of remote sensing prediction. Therefore the application of remote sensing techniques in the Dayaoshan Tunnel yielded notable results.
Introduction
The Dayaoshan Tunnel, 14.295 km long, is the longest double-track railway tunnel in China. Lying between pingshi and leeching in northern Guangdong Province, the tunnel cuts through the Nanling Mountains. Dense jungles, thick overburdens and concealment of most geologic features brought great difficulty in the tunnel survey. The construction started in 1981 and the tunnel was open to traffic in 1988 (Fig.1)
In order to check the result of the application of remote sensing techniques in thick forest zones of southern China, the Dayaoshan Tunnel was specifically selected as a test area for the application of remote sensing techniques. Beginning in 1981, large -scale black-and-white aerial, colour infrared, natural colour and black-and-white infrared photography, infrared scanning and multispectral scanning imagery were carried out in
the Daysoshan Tunnel area, and Landsat imagery and small-scale aerial photos were collected. In the study of the application of remote sensing techniques in the Dayaoshan Tunnel, eight spaceand serial remote sensing images were used. Through interpretations and analyses, more than 300 lineaments were determined with in the limits of 420 sq km in the tunnel area, and more than 40 lineaments were determined with in the limits of a 5km wide zone along the axis of the tunnel, of which 28 cut through the tunnel. The interpretation of remote sensing images provided a scientific basis and abundant geological information for analyzing the hydro geological condition in the tunnel.
In the course of the survey of the Dayaoshan Tunnel, drilling did not reveal substantial water, but macroscopic features of remote sensing images showed that the Bangu'ao trough in the central part of the tunnel had complex geological structure and adequate water-gushing conditions, thus providing information for the construction of the tunnel.
Topography and Geology
The "bowstring" portion (Fig.1) of the Wushui valley through which the Dayaoshan tunnel passes has a topographic relief of 300-1100 m. The Bangu'ao area in the central part of the tunnel is an elongate trough, 1-2km wide, with elevations of 400-600 m abovesealevel. This trough is flanked by lofty mountains. The Fangjinshi watershed on the east side and the Zhangzixian watershed on the west side both have an elevation of more than 1000m above sea level.
The strata exposed in the region consist mainly of Sinian and Cambrian (Z+
e) low-grade metamorphic elastic rocks, such as quartz sandstone, slate and carbonaceous shale, which are distributed in the medium low mountains at the entrance and exit of the tunnel. The Middle and Lower Devonian (D
1-2gt) quartz Sandstone and coglomerate is distributed in the watersheds on both sides of the Bangu'ao trough in the central part of the tunnel, and the Middle Devonian (D
2d) limestone and dolomitic limestone are distributed in the central part of the Bangu'ao trough.
From an analysis of geological structure, the Bangu'ao trough in the central part of tunnel is synclinal structure. The Core of the sycline is represented by Middle Devonian (D
2d) limestone, while its two limbs consist of middle and lower Devonian (D
1-2g1)quartz sandstone. The Jiufeng fracture transverses the tunnel along the centre of the Bangu'ao trough and then stretches southwards along the axial zone of the syncline. The fracture, as long as 30 km, is the largest fracture in the region.
